BOSTON – The Nets are staring extinction in the face. They don’t want to think beyond their next game, which they view as possibly their last game. They are using all the phrases: no tomorrow, do or die. All that stuff.

And that’s despite them holding the 3-2 advantage in the series.

So even with the one-game cushion, the Nets are taking the attitude that Game 6 of the Eastern Conference finals against the Celtics here tonight is more important than life or death. They’re treating it like a Game 7.

“[The Celtics’] season is not over yet, so they realize their backs are against the wall and they’ll come out swinging,” Kenyon Martin said. “I hope we have that same mindset. We’ve got to think there is only one game left in this series. We can’t think there is a Game 7. We have to think Game 6 is do or die. We get that attitude and their backs will really be against the wall.”

The Nets fear a Game 7 scenario and with good reason. Anything can happen. A turned ankle. A hot opponent. A cold shooting streak. So their attitude simply is don’t risk it. Finish the Celtics off tonight.

“I think they already know that [danger of a Game 7],” said Byron Scott, who gave his troops off yesterday in preparation for their first shot (OK, in their thinking, last shot) to advance to the NBA Finals. “Everybody on our team understands that we have a golden opportunity. Even though it’s on the road, we’ve proven that we can win there. We have a lot of confidence going on this road trip, so if there’s any way possible of getting it done [tonight], that’s what our goal is, to try to go up there and take care of business.”

The Celtics, of course, have other plans. Just as the Nets promised to be “wild dogs” when they faced the prospects of going down 3-1 after their historic Game 3 fold, the Celtics figure to be only slightly more rabid.

But Boston will be facing a Nets team that claims it has grown and undoubtedly has shown a new endgame toughness that simply wasn’t there before the playoffs. In each of the victories in Games 4 and 5, the Nets had to stand firm in the stretch. They won in Boston by a whisper. They won in the Meadowlands after appearing to crumble again as a 20-point lead plunged to one. Instead of crumbling, they employed a 20-1 run.

“We’ve emphasized what got us to this level and how we win games,” said Keith Van Horn, who crammed 11 of his 19 points into the fourth quarter of Game 5. “And No. 1 is our defensive intensity and that in turn will lead to rebounding effectively and that will allow us to push the ball and get into our offense. When we don’t defend, it takes our offense away from us, it takes our rebounding away from us, it takes our aggressiveness away. Our whole mindset and our whole energy comes from our play on the defensive end.”

And that’s what the Nets insist they must do tonight in Game 7. Er, Game 6.

“Our job is to try and win Game 6. That is the only thing we are thinking about, 5 and then 6,” insisted Jason Kidd. “You can’t think about 7, because you don’t want to go from 5 to 7. That means you weren’t listening in school about counting.”

But the Nets have learned about counting. And they’ve learned the dangers of letting a series run to its ultimate game. They did that against Indiana. All they needed there was double overtime to thwart Reggie Miller and the Pacers.

“We don’t want to do that again. Reggie is one guy that hits clutch shots and the Celtics have two plus some other guys,” said center Todd MacCulloch. “We don’t want to [play Game 7]. That is our motivation. That motivation needs to match how badly they need to win.”